Z Ursae Minoris (Z UMi) is a carbon star and R Coronae Borealis variable in the constellation Ursa Minor located about away.
Z Ursae Minoris was discovered to be a variable star in 1934. It was catalogued as a probable Mira variable, due to its red colour and variations over several hundred days. It was discovered to be a carbon star in a survey published in 1985, and subsequently found also to be hydrogen-deficient. After fading by almost six magnitudes in 1992, it was classified as an R Coronae Borealis variable. It was confirmed as an R Coronae Borealis variable, one of the coolest in the class, after its spectrum was analysed in 2006.
Its apparent magnitude varies between 10.8 and 19.0, representing a nearly 2000–fold change in brightness. Since Z UMi is located less than 7 degrees away from the North Celestial Pole, it is a circumpolar star for mid-northern latitudes allowing year round tracking.
References
External links Z Umi lightcurve at AAVSO